Optical Activity in the Near‐IR Region: The λ=980 nm Multiplet of Chiral Yb³⁺ Complexes

Abstract

We used a very simplified electrostatic model based on charge and polarizability of atoms and groups on an organic ligand around a lanthanide ion to predict the near-infrared electronic circular dichroism (NIR ECD) spectra of Yb (a monoelectronic ion). We tuned our method by using two widely different complexes. The first was the heterobimetallic species CsYb(hfbc) [hfbc=(-)-3-heptafluorobutyrylcamphorate], in which the ligand is a diketonate and, as such, is endowed with a chromophore with strong UV absorption (π-π ). Its oxygen atoms define a square antiprism, which provides a symmetric coordination polyhedron. The second system was Yb DOTMA [DOTMA=(1R,4R,7R,10R)-α,α',α'',α'''-tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid], a chiral Yb analogue of Gd DOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), in which the ligand lacks relevant electronic transitions and provides a dissymmetric cage. The relative weights of dynamic (ligand polarization) and static contributions to Yb NIR ECD were evaluated, and the spectra appear to have been well predicted by theory through the introduction of a heuristic weight factor. To validate the approach and to confirm the value of the weight factor, we applied it to two other compounds, namely, Na Yb(BINOLate) and Yb(BINOLAM) [BINOLate=2,2'-dihydroxy-1,1'-binaphthyl; BINOLAM=3,3'-bis(diethylaminomethyl)-1-1'-bi-2-naphthol].

Luminescence, chiroptical, magnetic andab initiocrystal-field characterizations of an enantiopure helicoidal Yb(iii) complex

“…This mixing of configurations allows gaining electric dipole intensities for the 4f-4f transitions by breaking the parity rule. 32 Such a procedure was successfully applied recently to obtained the CPL spectrum of an analogous Eu(III) tris -dipicolinate complex. 33 At 0 K, the calculated CPL spectrum exhibits a strong positive and a strong negative band corresponding to the 0' → 0 and 0' → 1 transitions, respectively.…”

Near-infrared circularly polarized luminescence from chiral Yb(iii)-diketonates

“…This apparent violation of the sum rule can be rationalized by taking into account that these f-f transitions gain rotational strength by coupling with the induced electric dipole transition moment of the π-π* transition on the diketonate moieties (dynamic coupling). 2,24,25 Therefore, such transitions can no longer be considered isolated and sum rule needs not apply.…”

Synthesis, Structural Characterization, and Chiroptical Studies of Bidentate Salen‐Type Lanthanide (III) Complexes

“…To simulate the same spectrum, we used Richardson's equations, a simplified electrostatic model based on charge and polarizability of atoms and groups of an organic ligand around a lanthanide ion . Charge and polarizability were evaluated respectively by standard natural bond orbital (NBO) analysis (from DFT calculations) and the atom‐based method by Miller .…”

“…Additionally, ECD spectra may be simulated by various approaches. For example, ligand‐centered ECD may be evaluated by means of time‐dependent Density Functional Theory (TD‐DFT), while a simple approach based on Richardson's equations provides an estimate of the metal‐centered Near‐IR ECD of Yb 3+ . The predicted spectra may then be compared with the experimental data, validating the solution geometry obtained from paramagnetic nuclear magnetic resonance (NMR) analysis …”

“…To simulate the same spectrum, we used Richardson's equations, a simplified electrostatic model based on charge and polarizability of atoms and groups of an organic ligand around a lanthanide ion. 22 Charge and polarizability were evaluated respectively by standard natural bond orbital (NBO) analysis (from DFT calculations) 46 and the atombased method by Miller. 47 The CD spectrum was simulated weighting each transition by the Boltzmann population of the starting crystal-field sublevel and applying to each line a Lorentzian function with Δν = 50 cm À 1 .…”